Revision of EOM Flashcards
1
Q
Define the terms agonist, antagonist, and contralateral synergist?
A
- Agonist – muscle producing movement
- Antagonist – movement in direction opposite that produced by agonist
- Contralateral Synergist – muscles that cause the 2 eyes to move in same direction
o i.e. yoke muscles RMR & LLR
o Underaction of one muscle, its yoke (paired) muscle overacts
2
Q
Define the terms DUCTIONS, VERSIONS, and DISJUGATE?
A
- Monocular movements are DUCTIONS
o Of uncovered eye when move torch round to side - Conjugate movements are VERSIONS
o What we are testing w/ torch aka smooth pursuits - Vergence movements are DISJUGATE
o Eyes moving in opposite directions
o i.e. convergence & divergence
3
Q
What are A & V Patterns?
A
‘V’ Patterns –> wider at top (SR underaction)
V pattern Exotropia – greater deviation in up gaze than down gaze
V pattern Esotropia – greater deviation in down gaze than up gaze
‘A’ Patterns –> wider at bottom (IR underaction)
A pattern Exotropia – greater deviation in down gaze than up gaze
A pattern Esotropia – greater deviation in up gaze than down gaze
4
Q
Describe the medial rectus muscle?
A
- Shorter & strong muscle
- Originates on both upper & lower limb of common tendous ring & optic nerve sheath
- Inserts along vertical line 5.5mm from cornea the horizontal plane of eye bisects the insertion
- Fascial expansion from muscle sheath forms the medial check ligament & attach to medial wall of orbit
o If get problems with medial wall of orbit, MR can be restricted in its movements - Innervation is via CN3, oculomotor nerve, & the specific branch runs along inside of muscle cone, on lateral surface
- Superior oblique, ophthalmic artery & nasociliary nerve all lie above MR
o Nasal sinus is near it - Inferior oblique is beneath it
- Origin: annulus of Zinn
- Insertion: medially, in horizontal meridian, 5.5mm from limbus
- Direction: 90°
- Innervation: lower CN3
- Blood supply: Inferior Muscular Branch of Ophthalmic Artery
- Action: adduction – inwards to middle
5
Q
Describe the lateral rectus muscle?
A
- Originates on both upper & lower limb of common tendonous ring & a process (attachment) of greater wing of sphenoid bone
o Greater risk from head trauma - Inserts parallel to MR 6.9mm from cornea – tendon 9.2mm wide, 8.8mm long
- Fascial expansion from muscle sheath forms the lateral check ligament & attach to lateral wall of orbit at Whitnalls tubercle holds it in place
- Innervated by abducens nerve (CN6) enters muscle on medial surface (closer to eye)
- Lacrimal artery & lacrimal nerve run along superior border of LR
- Abducens nerve, ophthalmic artery & ciliary ganglion lie medial to LR & between it & optic nerve
- Lateral wall is at side of it, superior rectus is above it, inferior rectus is below it
- Origin: annulus of Zinn
- Insertion: laterally, in horizontal meridian, 6.9mm from limbus
- Direction: 90°
- Innervation: CN 6
- Blood supply: Inferior Muscular Branch of Ophthalmic Artery
- Action: abduction or outwards or laterally
6
Q
Describe the superior rectus muscle?
A
- Sits on top of eye & moves it up
- Originates on superior limb of tendonous ring & optic nerve sheath
o If get inflammation towards back of optic nerve can get pain when move eye up - Muscle passes forward underneath levator, but the 2 lower sheaths are connected resulting in coordinated movements
o Levator on top of SR and superior oblique below SR - Insertion 7.4mm from limbus & obliquely
- Angle from origin to insertion is 23° beyond sagittal axis
o Because muscle runs at angle to the Fick’s axis, contraction is not confined to one axis - Frontal nerve runs above SR & levator
- Nasociliary nerve & ophthalmic artery run below
- Tendon for insertion of superior oblique muscle runs below anterior part of SR
- Innervations via superior division of CN3, from inferior surface; additional branches make their way to levator (gives lid some function)
- Action of SR:
o Primary action is elevation
Eye will sit low if issue with SR
o Since insertion on globe is lateral as well as superior, contraction will produce rotation about the vertical axis toward midline
o Secondary action is adduction
o Because insertion is oblique contraction produces torsion nasally intorsion - Pathway:
o To left & underneath SR is MR & medial wall
o To right is LR
o Superior division of CN3 inserts underneath it
o Underneath it is SO tendon
o Above it is levator & ophthalmic artery - Origin: annulus of Zinn
- Insertion: superiorly, in vertical meridian, 7.7mm from limbus
- Direction: 23°
- Innervation: upper CN 3
- Action: elevation, intorsion, adduction
SR has SO under it
7
Q
Describe the inferior rectus muscle?
A
- Short muscle
- Originates on lower limb of common tendonous ring
- Inserts 6.7mm from limbus, insertion is an arc
- It is parallel to superior rectus, making a 23° angles beyond sagittal axis
- Innervated by inferior division of CN3 which runs about it – within muscle cone
- Below is floor of orbit & IO
- Fascial attachments below attached to inferior lid coordinate depression & lid opening
o If operate on IR can risk giving px droopy lower lid - Fascia below IR & IO contribute to suspensory ligament of lockwood
o Ligaments move lids down when look down & up when look up - Primary action: downward gaze depression
- Pathway:
o Directly above is LR
o Inferior branch of CN3 gives its blood supply
o Underneath is floor of orbit
o Above it is optic nerve - Origin: annulus of Zinn
- Insertion: inferiorly, in vertical meridian, 6.5mm from limbus
- Direction: 23°
- Innervation: lower CN 3
- Action: depression, extorsion, adduction
- IR is distinctly bound to lower eyelid by fascial extension from its sheath
IO goes on outside of IR
8
Q
Describe the superior oblique muscle?
A
- Anatomical origin is on lesser wing of sphenoid bone
- Almost more tendon than muscle
- Physiological origin is the trochlea, a cartilaginous “U” on superior wall of orbit
- Longest thinnest EOM – muscle ends before trochlea
o Tendon is 2.5cm, smooth movement through trochlea - Innervation by CN IV – the trochlear nerve posterior in orbit
- Primary action is depression & intorsion
- Since insertion of oblique muscle is in lateral, posterior quadrant, the other actions are:
o Rotating back half of globe from lateral to medial (anterior poll will move away) ABDUCTION
o Depression – posterior superior quadrant of globe being pulled upwards - Origin: outside superior of annulus of Zinn (func. At trochlea)
- Insertion: posteriorly to equator of eye in supratemporal area
- Blood Supply: ophthalmic artery
- Innervation: CN 4 (trochlear)
- Action: intorsion, depression, abduction
- Pathway:
o Starts outside tendonous ring
o Moves forward up under roof of orbit towards cartilage area (trochlea)
Just before gets here it changes into a tendon
o No muscle in contact with eye – all tendon - Trochlea nerves supplies its under side
- Ophthalmic artery supplies is under side
- Brown Syndrome:
o Notch or swelling near trochlea
o Can move eye down but cannot move eye up because eye cannot retract backwards
o See in young children or can be acquired in people with arthritis
SR has SO under it
9
Q
Describe the inferior oblique muscle?
A
- Works in opposite to SO
- Originates on maxillary bone inferior to nasolacrimal fossa
o ONLY EOM originating in anterior orbit - Inserts on posterior lateral aspect of globe mostly inferior, below anterior-posterior horizontal plane
- Innervation from inferior division of CN3 inserts on upper surface (close to eye)– within muscle cone
o Shares nerve supply w/ MR & IR - Like a sling – is underneath eye and almost holds it
- Inserts quite close to macula at back of eye
- Primary action is elevation then extorsion then abduction
- 2° is due to posterior, lateral, inferior insertion being pulled around, underneath globe & toward anterior inferior insertion medially
- Rotation about Z axis will be nasal to temporal abduction
- Rotation about X axis will be elevation
- Origin: behind of lacrimal fossa
o Lacrimal fossa is where tear sac is - Insertion: posteriorly to equator of eye in macular area
- Direction: 51°
- Innervation: lower CN 3
- Action: extorsion, elevation, abduction
IO goes on outside of IR
10
Q
Describe the levator palpebrae superioris muscle?
A
- Origin: above of annulus of Zinn
- Insertion: above & anterior surface of tarsus
- Innervation: upper CN3
o Shares nerve supply with SR so if SR does not work, check lid too - Action: eyelid elevation
11
Q
Describe the obicularis muscle?
A
Part of face muscles, supplied by CN7.
V strong muscle – if squeeze eyes shut & someone tries to open them then it will be difficult
12
Q
What is the surgical consideration to be made when going to do surgery on EOMs?
A
- Blood supply to EOMs provides almost all of temporal ½ of anterior segment circulation & majority of nasal ½ of anterior segment circulation
o Therefore, simultaneous surgery on 3 rectus muscles may induce anterior segment ischaemia, particularly in older pxs
13
Q
What is the range of action of the eye?
A
- Globe usually can be moved about 50° in each direction from primary position
- Under normal viewing circumstances, eyes move only about 15°-20° from primary position before head movement
14
Q
Describe RADSIN?
A
RADSIN – Recti ADduct, Superiors INtort
Only applies to vertical muscles – vertical rectus muscles will adduct, vertical obliques will abduct
Superior rectus & superior oblique Intort
Inferior rectus & inferior oblique extort
15
Q
What is Herring’s Law?
A
Law of equal innervation – eyes have to move equally & simultaneously – each eye needs to receive same amount of energy to move eyes in same direction (LAW OF 2 EYES)
Needs synchronicity on eye movements 2 muscles contract, 2 muscles relax
SR & IO work in synergy (together)
